Pulp bleaching



Feb- 27, 1962 c. K. TExToR 3,023,140

PULP BLEACHING Filed Nov. 24, 1958 INVENTOM c2 avro/v /a 75x70@ 3,023,140 PULP BLEACHING Clinton K. Textor, Springfield, Ohio, assignor, by direct and mesne assignments, of one-half to The Bauer Brothers Company, Springfield, Ohio, a corporation of Ohio, and one-half to FMC Corporation, a corporation of Delaware Filed Nov. 24, 1958, Ser. No. 775,838 Claims. (Cl. 162-24) This invention relates to improvements in procedures for the manufacture of wood pulp more particularly the bleaching thereof. It provides a reiner-bleach process which obviates the need for separate bleach operations or special bleach apparatus in producing wood pulp and is particularly advantageous in application to mechanical pulp. Other distinctive advantages obtain which will become evident from the disclosure herein. While the invention will be specifically described with reference to the production of mechanical pulp from chips, it will be readily obvious to those versed in the art that the area and manner of application of the renner-bleach technique provided is not so limited. f

There is an increasing shortage of suitable wood for producing wood pulp to meet the needs and requirements of the pulp paper industry. Moreover, power cost in the production of wood pulp is constantly increasing. Thus, a basic dual problem exists. The result is a need for improvements in production procedures to enable the expansion of the base of suitable woods which may be used in the industry and there is a further need to provide more economical and efficient refining and bleaching procedures.

The above problems are particularly evident in the production of groundwood. This has traditionally been a high yield process which requires cheap power but high quality, light colored softwood. While it is a high yield process, the pulp and paper industries have previously looked upon the product as low grade due to its relatively weak strength. However, groundwood is an essential pulp and the growingcost of its production seriously affects the industry. A procedure for producing groundwood from chips so as to utilize maximum percentages of the suitable wood available promises to alleviate the above indicated problems in part but this alone is insuiiicient. Procedures further expanding the base of suitable woods as well as production economy are essential to stabilize the industry.

The present invention is directed to solving and/or minimizing the noted problems developing in the pulp and paper industries. This is accomplished by an improved retiner-bleach technique. The conventional procedure in producing groundwood is to completely refine wood pulp then bleach it in an entirely separate operation employing special bleach equipment. In the alternative, a more recent proposal suggests the actual incorporation of bleach equipment in the refining process at a particular intermediate stage whereby to eliminate the use of conventional bleach towers. In either instance the labor and equipment essential to the bleaching portion of the process is relatively costly. The present invention completely eliminates special bleach equipment and procedure. It enables an effective bleaching of wood pulp utilizing ordinary refining equipment without the need for any special digesters or conventional bleach towers. Moreover, by the inventive procedure the nature and variety of wood which may be employed for the production of groundwood is substantially expanded, while the power consumption is substantially reduced. A particular feature to note is that the technique provided has proven to inherently develop the strength of the groundwood product resulting without materially affecting its other desirable qualities. Thus it may be readily seen that not only are substantial economies produced by the invention but also the desirability of the groundwood product is enhanced.

A primary object of the invention is to provide a simpliiied and improved procedure for manufacturing bleached wood pulp rendering such products more economical to produce, more efficient and satisfactory forV use, adaptable to a wider variety of applications and more distinctive in desirable characteristics.

A further object of the invention is to provide a novel renner-bleach technique for producing mechanical pulp.l

Another object of the invention is to provide a refinerbleach process for wood pulp eliminating the need for special bleach apparatus o-r special bleach procedure in the production thereof.

An additional object of the invention is to provide a simplified method of producing groundwood which substantially expands the amount of wood suitable for use in the production thereof.

A further object of the invention is to substantially reduce the power and space requirements for producing Wood pulp, particularly groundwood.

Another object of the invention is to provide an im-' proved refiner process for producing wood pulp whichV provides an increase in the pulp strength as well as a bleaching thereof employing ordinary refining equipment.

A further obJ'ect of the invention is to provide a refinerbleach technique for use in producing wood pulp possessing the advantageous elements, the inherent meritorious characteristics and the mode of operation and application herein defined.`

With the above and other incidental objects in view as will more fully `appear in the specification, the invention intended to be protected by Letters Patent consists of the features of construction, the parts and combinations thereof, andthe mode of operation as hereinafter described or illustrated in the accompanying drawings, or their equivalents. i

Referring to the accompanying drawing wherein is shown one but obviously not necessarily the only form of embodiment of the invention,

FIG. 1 shows a block type flow diagram illustrating a refiner-bleach technique in `accordance with the invention;

FIG. 2 shows a block flow diagram illustrating a basic pulp production procedure in accordance withv the invention; and

. FIG. 3 illustrates a modification of the procedure shown in FIG. 2.

FIG. l shows a preferred procedure for the production of groundwood from chips in accordance with the invention ywherein bleaching is effected simultaneously with the refining of the pulp. The invention procedure provides a four stage refinement. The refiners a-re preferably of the disc mill type and are respectively numbered 1, 2, 3 and 4.

Wood chips suitably prepared are introduced in 'a fluid medium, water being indicated as the vehicle, to a first stage refiner 1. Simultaneous with the introduction of the chips in the fluid medium 1.0% sodium tri poly phosphate, a sequestering or chelating agent, is introduced. The purpose of the sodium tri poly phosphate is to initially inactivate iron compounds and other chemicals present'which might cause a darkening of the pulp in the refining procedure. The first stage refiner p-roduces a rough breakdown of the chips and intermixes the sequestering agent.

The mixture is passed from refiner 1 through a second stage disc refiner 2 which insures a complete mix of the inactivating agent. KIn some instances the refiner 2 will Patented Feb. 27, 1962.

be unnecessary but its presence is desirable as a safety factor.

The mixture resulting is then passed from the refiner 2 to the refiner 3. Additional water, a 1.0% hydrogen peroxide solution and .05% magnesium sulfate is introduced to the refiner 3 with the mixture. In this third pass, refining is effected in the presence of the bleaching agent hydrogen peroxide. The magnesium sulfate stabilizes the peroxide bleach liquor.

As the partially bleached refined pulp is introduced into refiner 4 for its-fourth refining pass, a 1.0% sodium hydroxide solution and 5.0% sodium silicate solution is added to the mixture. During the fourth pass, the sodium hydroxide produces an interaction with the hydrogen peroxide `already present to accelerate the bleaching action and it simultaneously softens and increases the strength of the pulp'fibers in the refining action.

This refining procedure provides a refinar-bleach technique producing a pulp which has been bleached during the refining process. No further bleaching procedure or special bleaching equipment was or need be employed. The results are equivalent to a complete refining procedure followed by a bleaching operation. There is likewise equivalent brightness, even` with minimum processing. Moreover, the chemicals as applied enable the utilization of many hardwoods not previously suitable for the production of gronndwood. In Vthe development of this refinerbleach procedure it 'was also found that the addition of the chemicals reduced the power necessary to fiberize the chips and the pulp resulting and in addition caused a substantial increase in the pulp strength.

Thus, the inventive procedure affords a simultaneous renner-bleach technique which avoids usage of any digester or special bleach equipment and produces pulp products equivalent in brightness to conventionally produced pulp. The products resulting are also substantially greater in strength and capable of being produced using woods not previously considered suitable for the production of groundwood. Substantial savings in time, labor and equipment are accomplished enabling a reasonable price of the pulp products for the paper and pulp industry. The invention also insures adequate supply of groundwood with a character of brightness and strength which substantially expands the field of desirable application thereof.

It is noted that groundwood has the highest opacity of all available pulp and is particularly good for its printing quality. Therefore, while groundwood previously was most commonly used in newsprint paper and box board, the increase in its strength by the invention. procedure as well as its economy due to the reduction of power consumption in the process and the combining of the refinerbleach procedures causes the groundwood pulp product to be much more attractive to the industry. The invention procedure is also capable of application to the other areas where costs are of significant importance.

The renner-bleach technique of the invention is not confined in application to mechanical pulp from chips but may be also used in the production of conventional groundwood. It has been proven in mill refining in the presence of bleach liquor that the resulting product, after acidifying, will generally have strength and brightness properties at least equivalent to conventionally prepare bleached groundwood. To summarize, the invention reduces capital cost, cost of production, increases pulp strength and provides pulp to paper industry which has increased flexibility of application.

Referring to FIGS. 2 and 3 of the drawings, a broader aspect of the invention is presented therein. FIG. 2 shows a ow diagram wherein chips in a fluid medium are passed through two refiner stages preliminary to passage through a washer. In this broad/concept of the invention, simultaneous with the introduction of the chips in a fluid medium to the first refiner l', both sodium hydroxideand hydrogen peroxide are introduced. In the refining procedure there is a direct interaction of the chemicals with the pulp under the infiuence of and as a consequence of the refining action. The sodium hydroxide also acts to soften the wood, enabling the chips to be fiberized with one half the power conventionally required and causes an increase in fiber strength of a substantial nature in the process. The bleached pulp then passes from the first to the second refiner 2' wherein a continuing intermixture and bleach reaction takes place simultaneously with the refinement. The resultant product is then conventionally passed through a washer to provide a bleached pulp of a strength which is substantially greater than conventional prepared pulp and a brightness which is at least equivalent to conventionally prepared pulp. yThe product cost is minimized.

FIG. 3 is similar to FIG. 2 with the exception that the hydrogen peroxide alone is introduced with the chips in a uid medium into the first refiner 1" to start a bleach reaction as it is intensively mixed in the refining procedure. The sodium hydroxide is introduced in the second refiner 2 to then accelerate the completion of the bleach reaction. The results are similar asin the instance of the procedure of FIG. 2. In either event the product is provided with a minimum of required power. The bleaching medium accomplishes this and simultaneously effects a bleach of the pulp to necessary brightness without the need of any special digesters or separate bleach towers. The utilization of the sodium hydroxide or its equivalent distinctively enables the employment of hardwood as well as softwood in the production of groundwood.

The invention has been illustrated in preferred form herein. The percentages and sequence of the chemicals applied are preferred but not restrictive, depending on the application. 'lhe invention opens a whole new concept in the production of bleached wood pulp and particularly enlarges the application of groundwood. The novelty present is not intended to be construed in any limited manner but is intended to have a scope and teaching consonant with the improvement and advantages afforded the art thereby.

From theV above description it will Ibe apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desir-able, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts Without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with `the statute the invention has been described in language more or less speciclas to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise but one of several modes of putting the invention into effect, and the invention is therefore claimed in lany of its forms or modifications within the legitimate and valid scope of the appended claims.

Having thus described my invention, I claim:

l. In a continuous process for producing bleached pulp from wood chips including the steps of passing raw wood chips in a fiuid through a succession of refiners for staged reduction thereof to a desired pulp consistency, the irnprovement of adding bleaching chemicals to the refiners to thereby 'provide simultaneous refining and complete bleaching ofthe pulp in staged fashion before discharge from the refiners.

2. A process for producing bleach pulp from Wood chips including the steps of passing raw wood chips in a uid through -a staged refiner system, characterized by addingV bleaching and softening agents to the pulp and thoroughly .intermixing them with the pulp in the refiner system at selected stages and producing completely bleached pulp of substantial strength in the process.

3. In a continuous process for producing bleached pulp from Wood chips including the steps of passing raw wood chips in a fluid through a succession of refiners for staged reduction thereof, the improvement of chemically modifying the pulp preliminary to passage thereof through selected reners to inhibit darkening of the pulp and injecting bleaching agents in the pulp for passage with the pulp through the refiners to effect a staged bleaching of the pulp, the intermixture of the chemicals being accelerated by the refiners, and completely bleaching the pulp during said passage through the refiners.

4. A process for producing bleached wood pulp from wood chips including the steps of mechanically fiberizing raw wood chips in the presence of a bleaching agent to produce a thorough intermixture of the bleaching agent and the Wood fibers and further refining the wood chips in the presence of an accelerating agent to simultaneously soften the fibers and reduce power consumption necessary for refining and producing a completely bleached pulp during the process.

5. In a renner-bleach technique including the steps of successively passing -raw wood chips through a plurality of refining stages, the improvement of adding a sequestering agent, a bleaching agent in conjunction with a stabilizing medium, and an accelerating agent to selected refiners `for passage through succeeding rening stages simultaneously with the chips, to thereby produce a complete bleaching and strengthening of the pulp during the refining process.

6. A refiner-bleach technique including the steps of introducing raw wood chips in a fluid in the presence of hydrogen peroxide or the like to ya refiner to simultaneously fiberize the chips and intermix the hydrogen peroxide to initiate the bleaching of the pulp, further introducing a bleach accelerator to soften and strength the pulp and subsequently refining the pulp further to thereby accomplish a complete bleachin and strengthening of the pulp during the rening process.

7. In a continuous reiiner-bleach process for producing bleached pulp, the improvement of introducing raw Wood chips and sequestering agent in a fluid to a refiner for intermixture thereof to inactivate chemicals which might darken the resultant pulp, introducing the resultant product to a subsequent refiner with a bleaching agent, providing a thorough intermixture thereof and a bleaching of the pulp in the process, 'and simultaneously further refining the mixture of bleaching agent, sequestering agent, and Wood chips with a bleach accelerator to produce a completely bleached pulp simultaneously With the retining thereof.

8. In a continuous process for producing bleached pulp including 'the steps of passing raw Wood chips in a fluid through successive refiners for staged reduction 4thereof to a desired pulp consistency, the improvement of successively adding sodium tri poly phosphate, hydrogen peroxide and sodium hydroxide to the refiners for intermixture with the fibers, thereby providing ya continuous and simultaneous complete bleaching and refining of the pulp.

9. The process as set forth in claim 8 characterized by the addition of furthering sequestering and stabilizing agents to the fibers as they pass through the refiners to insure maximum color quality and strength to the resultant pulp product.

l0. A process for producing bleached pulp from raw Wood chips including the steps of pretreating the -raw wood chips with an aqueous solution and introducing the treated chips into a refining system comprising a series of successive refiners, characterized by the addition of bleaching chemicals to the chips at selected points in such system, such points being so selected that `the chips are subjected to a refining action in the presence of the bleaching chemicals to provide simultaneous refining and complete bleaching of the pulp before discharge from the system.

References Cited in the file of this patent UNITED STATES PATENTS 1,775,405 Neuman Sept. 9, 1930 1,850,832 Ellis Mar. 22, 1932 2,125,634 Heritage Aug. 2, 1938 2,187,016 Craig Jan. 16, 1940 2,413,583 Shearer Dec. 31, 1946 2,435,566 Adams et al Feb. 10, 1948 2,465,738 McEwen Mar. 29, 1949 2,492,047 KBurg et al. Dec. 20, 1949 2,707,144 Sparrow Apr. 26, 1955 2,717,195 Armstrong Sept. 6, 1955 

2. A PROCESS FOR PRODUCING BLEACH PULP FROM WOOD CHIPS INCLUDING THE STEPS OF PASSING RAW WOOD CHIPS IN A FLUID THROUGH A STAGED REFINER SYSTEM, CHARACTERIZED BY 